This invention relates to a milling tool designed to form a semi-circular cross-sectioned groove in a work piece. The groove may be used as a ball track in a ball screw element. Other uses are possible. Tools for a similar purpose are shown in U.S. Pat. No. 4,423,989 issued to Kress, et al., and U.S. Pat. No. 4,566,828 issued to J. Reinauer.
The milling tool of the present invention comprises a rotary spindle (shaft) having an axially-extending slot in its end surface. A circular cutter plate fits into the slot so that at least one half of its circular cutting edge projects beyond the spindle. The peripheral edge of the cutter plate is subdivided into four segmental arcuate cutting edges, with alternate cutting edges facing in opposite directions.
During powered rotation of the spindle around its axis, two of the segmental arcuate cutting edges are exposed to the work surface. The other two cutting edges are located within the spindle slot for later use (when the two exposed edges become dulled or worn). Each exposed segmental cutting edge performs a cutting function on one half of the engaged work piece surface.
A principal feature of the invention is a cutter plate holder means that effectively utilizes shoulder surfaces on the cutter plate for precisely retaining the cutter plate in a centered position. The term "centered position" refers to a position in which the separation point (line) between the two exposed segmental cutting edges is located precisely on the axial midplane of the spindle (shaft). With this centered arrangement, each segmental cutting edge achieves the same cutting action in a balanced condition. The cutter plate holder means includes a post construction that accurately orients the cutter plate holder means to the rotary spindle. The post construction constitutes a relatively low cost mechanism for properly orienting the cutter plate holder means.